1. Field of the Invention
The present invention relates to an internal combustion engine component, e.g., a cylinder block or a piston, and a method for producing the same. More particularly, the present invention relates to an internal combustion engine component composed of an aluminum alloy which includes silicon, and a method for producing the same. The present invention also relates to an internal combustion engine and a transportation apparatus incorporating such an internal combustion engine component.
2. Description of the Related Art
In recent years, in an attempt to reduce the weight of internal combustion engines, there has been a trend to use an aluminum alloy for cylinder blocks. Since a cylinder block is required to have a high strength and high abrasion resistance, aluminum alloys which contain a large amount of silicon, i.e., aluminum-silicon alloys having a hypereutectic composition, are expected to be promising aluminum alloys for cylinder blocks.
In a cylinder block composed of an aluminum-silicon alloy, silicon crystal grains located on the slide surface will contribute to the improvement of strength and abrasion resistance. An example of a technique for obtaining silicon crystal grains exposed on the surface of an alloy matrix is a honing process for allowing silicon crystal grains to remain jutting (called “emboss honing”). Moreover, Japanese Patent No. 2885407 discloses a technique of performing an etching process for allowing silicon crystal grains to remain jutting on the surface of an aluminum-silicon alloy, and thereafter performing an anodic oxidation to form an oxide layer, and further flame spraying a fluoroplastic onto this oxide layer to form a fluoroplastic resin layer.
Since a lubricant is retained in between the silicon crystal grains which remain jutting on the slide surface (i.e., in the recesses between the silicon crystal grains functioning as oil puddles), an improved lubricity is obtained when a piston slides within the cylinder, whereby the abrasion resistance and burn-up resistance of the cylinder block are improved.
However, the inventors have found that further improvements in abrasion resistance and burn-up resistance become necessary when using the above-described aluminum-alloy cylinder block for certain types of internal combustion engines.
Conventionally, aluminum-alloy cylinder blocks have been used in internal combustion engines that are mounted in four-wheeled automobiles. In a four-wheeled automobile, a mechanism (e.g., an oil pump) for compulsorily supplying a lubricant for the cylinder block and piston is provided in the internal combustion engine, and the internal combustion engine is operated at a relatively low revolution speed (specifically, under a maximum revolution speed of 7500 rpm or less), in which case the aforementioned problems will not occur. However, in an internal combustion engine which is operated at a relatively high revolution speed (specifically, under a maximum revolution speed of 8000 rpm or less), or in an internal combustion engine in which a lubricant is supplied to the cylinder only by way of splashing of the lubricant associated with crankshaft rotation (i.e., the oil pump is omitted, as in the case of an internal combustion engine that is mounted in a motorcycle), the aluminum-alloy cylinder block may experience burn-up and/or significant abrasion. Moreover, when an aluminum alloy is used as the piston material in order to achieve a further mass reduction, there is an increased likelihood of burn-up.
In order to further improve the abrasion resistance and burn-up resistance of the cylinder block, it is necessary to improve the lubricity at the start of the internal combustion engine, which requires good retention of lubricant on the slide surface. The inventors have found through their study that a cylinder block which has been subjected to the aforementioned emboss honing process or etching process cannot achieve a sufficient lubricant retention, so that less than adequate lubricity exists when a high-speed operation is reached immediately after the start of the internal combustion engine.